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I 878A
ANALYTICAL CWMISTRY, VOL. 57, NO. 8, JULY 1985
Over several decades chemical tests for intoxication have become commonplace in a wide range of criminal and civil cases. Proof of one’s blood alcohol concentration (BAC) is regularly admitted in simple operating-underthe-influence (OUI) cases, in motor vehicle homicide and manslaughter cases, and in serious accident and death cases. BAC evidence is now appearing frequently as well in life insurance benefit cases, in “dram shop” cases where taverns and restaurants are charged with liability for serving intoxicated patrons, and in “guesthost” cases where a host can be held liable for providing an excessive amount of alcohol to a guest in his or her home. The criminal and civil liability of the driver is a t stake, and benefits recoverable by a spouse, children, other passengers, and other accident victims often depend on the ultimate interpretation given a single BAC value. The proper role of BAC test results is often forgotten in the actual trial of such cases. In nractice. the BAC result has become “the” critical evidence. Unfortunately, the true, limited significance of a single BAC test is often misstated in the courtroom ( I ) . When complex scientific concepts are oversimplified for forensic purposes, a true understanding of the biochemical processes is often lost. Even many courtroom experts are unaware of those important principles that originally limited, and that ought still to circumscribe, the opinions they offer. As a result, miscarriages of justice do occur, and the innocent can be convicted along with the guilty. Whereas scientists tend to think in terms of populations, groups, averages, and trends, lawyers must think in terms of the guilt or innocence of the individual. Many “close” cases do come before the court where the “influence” is questionable. Opinion evi0003-2700/85/0357-876A$Ol.50/0 @ 1985 American Chemical Society
ReDort David N. Hume Edward F. Fitzgerald
W“ DO THE NUMBERS REALLYMEAN? dence, based on one BAC sample collected one to three hours after the driving incident, may result in conclusions that are in many cases highly speculative, in others totally unfounded. Conclusions about the actual effect of a given BAC as applied to a chance person before the court, based largely on studies of the observed effects of alcohol on large population groups, can mislead rather than guide the trier of fact. Scientists, of course, want to be accurate when they testify in the courtroom. Quite understandably, however, they also want to help law enforcement to curb a major national prohlem. Scientists, no less than lawyers and judges, respond to pressure to advance “the war” against drunk drivers. The tendency to oversimplify concepts to do this has flourished because of the scientific illiteracy of most lawyers and judges, because of the partisan approach adopted by many expert witnesses, and because, quite simply, there is no lobby for drunk drivers. Many experts, as public employees, consider themselves part of the “police team.” Many researchers are funded by public monies allocated to this war by federal and state highway safety programs, which is entirely laudable and should continue. Unfortunately, in forensic practice, a police team mentality can result in poor science and worse law. As Galileo, and perhaps Oppenheimer as well, would remind us, the integrity of science can sometimes be compromised by a too eager desire to serve perceived public needs ( 2 ) . Some very troublesome practices have developed in the present use of BAC evidence. Typically, only one body sample is obtained (breath or blood). The purported BAC of a person at some earlier time is then deduced from that test sample. That same person’s condition in terms of
sobriety at the earlier time is also said to he “inferable” from that one sample. Many experts regularly offer “firm” opinions on questions of sobriety without any knowledge of the person’s alcohol tolerance, drinking hahits or experience, or about his or her food and drink consumption on the occasion in question. The degree of delayed absorption caused by food is unpredictable even when the conditions are reasonably standardized; the individual characteristics of the drinker represent the most important variable factor (3). Underlying the use of the present one-test approach are a number of assumptions: that alcohol is rapidly ahsorbed, that a peak BAC will he reached within 15 to 30 minutes after the last drink, that an individual arrested within the first half hour after drinking ends will he at or very near his or her peak, that after drinking stops a slow hut steady decline will take place, and that any delay hetween incident and test, even of several hours, will only benefit the defendant. These assumptions imply that any sample collected within a “reasonable time” after an incident can tell us that individual’s “time of incident” BAC. In fact, many studies have shown that a single later test is not a reliable indicator of the earlier BAC; nevertheless, the assumptions described continue to be used for that purpose. Further assumptions regarding an individual’s alcohol tolerance, driving experience, and general physical and mental condition are needed to speculate upon the effects that the estimated BAC would have had on that person on that particular occasion. Sometimes there is evidence to support such assumptions, sometimes not. In the majority of OUI cases, the total evidence of intoxicated behavior and impaired automobile operation may
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be very strong, and an inference that the earlier BAC was as high as, or higher than, a later test BAC might he justified. In many cases, however, there is little evidence apart from those arbitrary assumptions to support such an inference. It is important to understand the legal application of the measurable BAC to the measurable-effects relationship as incorporated in all of our OUI statutes with some variations in language. Legal inferences are created. In the great majority of jurisdictions, if the BAC value is 0.10%or more (0.08%in a few jurisdictions), the jury will be instructed that it may draw an inference that the subject was “under the influence.” This inferential level is frequently mischaracterized, even by lawyers, as “the legal limit,” implying that one over it is guilty or is under the influence, which is not true, either in fact or under our OUI laws. The inference created by OUI laws is rebuttable: An individual with a BAC over 0.10%may still be found not guilty in light of the other evidence. (In some states, however, new “per se” statutes have been adopted that make it a separate crime to drive with a BAC of 0.10% or more, even though there is no evidence that the alcohol has had any detectable effect upon the person.) The statutory inferences are now accepted almost without question. As a practical matter, in the absence of some extraordinary circumstances, once a test value above 0.10% is found, the defendant will he found guilty, and in civil suits the driver will he found negligent. Judges and juries are led to believe 0.10% means “drunk” (untrue), and they look to the BAC result, and to those associated inferences, as being nearly infallible. Because of increased criminal and civil penalties, trial lawyers have begun to reexamine the evidentiary questions and to reevaluate concepts that, large-
ANALYTICAL CHEMISTRY, VOL. 57, NO, 8. JULY 1985 * 877A
FIgure 1. Characteristics of the blood
alcohol concentration (BAC)curve Time lor tu11 abmplion ranges hom les3 than 30 minutes IOmors man thee n o m depending an p~esenceQ absmce 01 food In slomach; type 01 beverage: cabiic and a l ~ ~ n o l content ic 01 bsvwage: use 01 mixers. mle 01 consumption; yse of drugs or medicirea; phVaical and mental slam 01 drinker: a M lndivdual characl~i6liCs01 lhe drinker
ly by default, have become part of the conventional wisdom about the significance of BAC tests. Clearly, it is essential to find out how reliable the BAC test, upon whirh the court will rely, really is. T o do so, we must examine how the BAC comes into being. how it rises and falls, and how it is eliminated (Figure 1).
The rise and fall d the BAC It is imperative that BAC results be both reliable and interpretable. Accurate and precise methods are available for the measurement of alcohol in blood and breath samples. Commercial instruments of considerable sophistication have been developed for the purpose, based on gas chromatography, IH absorption. spectrophoto. metric measurement of chemical and enzymatic reactions, and electrochemical fuel cells. The conrentratiuns to be measured are low, bordering on trace analysis, yet many measurements are made by unskilled terhnicianx with limited understanding of the principles involved. The alcohol concentration in blood is usually expressed as percent w/v, Le., the grams of ethanol per 1 0 ml. of blood. multiplied by 100. Most samples fall in the range of 0.04% to 0.25%. The methods used are usually capable of reproducibility within about fO.OlOb. with well-maintained equipment and rompetent operators. U n fortunately, serious problems are involved both in obtaining valid samples and interpreting the analytical results. The human body is an exceedingly 878 A
complex, inhomogeneous dynamic system, and no two bodies are exactly alike. An individual’s BAC is constantly changing, and the BAC of interest is not that at the time the sample is collected, but rather the value at the time of accident or arrest. T o understand the nature of the BAC as a function of time, we must consider what happens in the body when alcohol is consumed. Alcohol is absorbed very slowly while in the stomach, but once it passes into the small intestine, it is rapidly absorbed into the bloodstream and carried to all parts of the body (Figure 2). If food is in the stomach, much of the alcohol is retained with it until the food is digested and moves on to the small intestine. Rates of digestion and stomach emptying vary greatly with individuals and with the kinds and amounts of food consumed. The rate of emptying of ordinary mixed meals is greatly influenced by fat content. A heavy meal with a high fat content may take four to six hours to be digested, with a corresponding delay in alcohol absorption. Alcohol on an empty stomach, however, tends to be absorbed completely in 20 to 60 minutes. The blood carries alcohol to all the organs and tissues of the body, where it is distributed in amounts proportional to their water content. Thus nerves, brain, and muscle achieve relatively high concentrations, whereas bone and fatty tissues absorb comparatively little. Alcohol is eliminated from the body mainly by enzymatic oxidation in the liver. A representative curve of BAC vs. time following rapid ingestion of a beverage such as gin or vodka on an empty stomach is shown in Figure 3, curve A. There is a rapid initial rise in the BAC: the rate of absorption decays exponentially with a half-life, in this instance, of about fib minutes. If there were no eliminatior the final BAC in this enamde would be 0.10%, but the liver is removing al coho1 at a rate that lowers the BAC 0.015% per hour-a typical value. Th resulting curve shows rapid increase, leveling off at about four half-lives fc lowed by an increasingly linear decline.
Wldmalk hypothesis Widmark (4), in a 1932 study involving only 30 people, developed a method for estimating from a single BAC measurement both the amount of alcohol consumed and the BAC at times prior to the test sample. His subjects were given a known amount of alcohol per kilogram of body weight, as a single dose on an empty stomach. He then took frequent blood samples to plot curves of the type shown in Figure 3, curve A. From the
ANALYTICAL CHEMISTRY. VOL. 57, NO. 8. JULY 1985
Flgure 2. Absorption and distribution of alcohol in the human body
slope of the straight line portion he could determine the rate of elimination, which he called 8. Extrapolation of the linear pojtion of the curve back to time zero gave the blood alcohol concentration that theoretically would have been reached if all the alcohol were absorbed and equilibrated instantaneously. From the body weight of the subject and the weight of alcohol consumed, Widmark could calculate the theoreti-
f 30
1 60 90 120 150 (min)
Flgure 3. Theoretical curves of EA against time
CUNe A. alcohol on all empty Stomach Curve 0. Uw same amoum of alcohol with food
(continued on p . 882A)
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Figure 4. Plot of Widmark‘s r factor against @ for his subjects Open ckcles, men: tilled ckclsa, women. Born rand 6 ahow wide Scans about Wlr avsragss with h mnelatlca between rand 6
sorbed than hard liquor and gives lower peaks with the same amount of alcohol. Attempts to calculate r from a beer curve can give ridiculous values that suggest that the whole-body alcohol concentration is greater than the concentration in the blood. The timing of sample collection is extremely important. An individual who has bad a number of drinks with a fairly heavy meal may not reach his or her peak BAC for one to three hours after the end of drinking. If, driving home after such a meal, one has an accident and is taken into custcdy, he is not likely to be tested for another 30 minutes to 2 hours after arrest. His BAC a t the time of the accident may have been well below 0.10% but significantly above that value by the time the test is taken. The prosecution automatically assumes that the BAC was falling, rather than rising, hetween the incident and test. Their experts will typically add 0.015% to the test value for each hour elapsed from arrest to test. Assume, for example, a slowly rising BAC that had reached 0.06% at incident time and a test BAC of0.1296 two hours later. Using the approach commonly employed by prosecution experts, that driver would be “estimated,” to have had a 0.15% timeof-incident BAC, an unconscionably unfair result by either scientific or legal standards. Such complications do not imply that single chemical tests for intoxication are necessarily worthless. A properly determined “ h i g h BAC can effectively refute the “two beer” defense. One high value, together with other substantial evidence of intoxica~
cal whole-body alcohol concentration (WBAC) a t time zero. The ratio of W A C to BAC be designated as “r.” If an individual’s BAC is measured at some point on the declining portion of the curve, and if his or her r value is known, then (BAC)(r) = WBAC in percent by weight. From the body weight and the total body alcohol, he estimated the weight of alcohol that “must” have been imbibed to give the observed BAC. To estimate the BAC a t some prior time (hut still after the peak), he applied a correction by adding 0.015% (his average value of B) to the test BAC value for each hour elapsed between the time of interest and the taking of the blood sample. Thus he calculated the BAC an hour or two earlier during the period of steady decline. Widmark was very well aware of the limitations of his method and the great uncertainties in the assumptions that had to be made when applying it. Unfortunately, although his approach and principles are still the foundation for such calculations, the limitations and uncertainties he noted are generally ignored. In actual cases, the value of the individual‘s r is never measured and is not known. Instead, Widmark’s population average, 0.68 for men, is assumed to apply to any chance subject. Even in Widmark’s small group, the r values ranged from 0.47 to 0.86, and the average for women was significantly lower than for men. Similarly, Widmark’s average 0 (0.015%),or a value close to it, is applied to all subjects, despite the fact that Widmark’s @’s spread quite evenly over the range of 0.010%to 0.020% (Figure 4). Later
studies with larger populations confirmed his findinas and showed results as low as 0.006% &d as high as 0.04096.
Numerous charts, tables, and calculating devices are in common use in many states. They are sometimes distributed by state officials or departments and are often used in alcohol education courses, and they purport to guide the drinking public as to the probable BACs to be expected after consumption of given amounts of alcohol. The calculations are based on the use of Widmark’s average r for men (0.68).As a result, they are dangerous when used by women or low-r men. The “probable BACs” in question can in fact be reached on considerably less alcohol than is suggested by the charts when used by low-r persons. The possibilities for error when estimating probable BACs, prior BACs, or alcohol amounts consumed are compounded if Widmark’s methods are applied in situations that do not correspond to his “model situation”-hard liquor in a single dose on an empty stomach (5). The wide range of BAC values found when Widmark gave his suhjecta the same amount of alcohol per kilogram of body weight is seen in Figure 5.Studies show that when alcohol is taken with a meal the rise in BAC is slower, and lower peaks are generally obtained (Figure 3, curve B). A drinker may hold hia BAC nearly constant for a period of hours when intake balances elimination. Roller coaster rises and falls in peaka occur over periods when drinking is intermittent. Beer presents separate calculation problems; it is less rapidly ab-
882A * ANALYTICAL CHEMISTRY, VOL. 57, NO. 8. JVLY 1985
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tion at the incident time, may conclusively eliminate the suggestion of other causes for the conduct observed. Conversely, the finding of a low or negligible BAC on one test may exculpate the subject or may support a suggestion of other causes for the ohsewed behavior. What is not proper, however, is the overinterpretation of a single data point to infer a specific prior BAC or amount of alcohol consumed. The significance of any BAC measurement must always be determined within the context of time as one point on a continuum and not as a static value. Although the procedure would not eliminate all interpretation problems, requiring a minimum of two tests, at least one half hour apart, would be of great value in assessing BAC results, and the time and expense would be minimal.
Breath testing For forensic purposes, the conversion of breath alcohol to BAC is statutorily required. Most tests offered in court are done on expired breath, rather than on blood, for many reasons. It is a noninvasive technique, it is rapid, it can be used in the field by police officers rather than medical or laboratory technicians. Unfortunately, all breath-testing devices are designed to permit uniform use with chance individuals from a large, heterogeneous population, and so certain assumptions are made about the tested individual that may or may not be true. To convert breath alcohol to BAC, a conversion factor of 21oO:l is used, on the assumption that 2100 mL of deep lung breath has the same weight of ethanol as 1mL of blood when the two phases are in equilibrium at normal body temperature. In fact, this is true for only a relatively small portion of the population. The value of 2100:l was the compromise achieved by a committee that examined the results of more than 25 studies in which averages ranging from 11421 to 34781 were reported, with individual values much higher and lower. This very wide range of values is understandable. Many significant variables in addition to experimental technique affect the result. Deep-lung (alveolar) air may or may not he in equilibrium with the blood. The sample of air taken from the mouth may or may not be representative of alveolar air. Variable amounts of tidal air may be present depending on the subject’s condition or on how long and hard the subject was persuaded to blow. The bronchial passages, throat, and mouth, through which the sample passes, all have moist surfaces that exchange alcohol with the breath as if it were a sample going through a chromatographic column. There is a suh-
’ stantial temperature gradient between mouth and lungs, and the temperature is in a range where the vapor pressure curve of ethanol is rising steeply. “Normal” body temperature is not a fixed value but covers a range of several degrees. Fever can elevate the alcohol content of the breath and the presence of drugs such as aspirin can lower it significantly. Other factors, such as the hematocrit, can also affect the result. Althoueh the use of the factor z1o0:i toconvert breath to BAC may give a fairly reasonable estimate for many people, there are a substantial number who may be falsely convicted or improperly exonerated by the result. Mason and Dubowski (6),who are recognized experts on breath analysis, say simply that the true value, if indeed there is such, lies somewhere in the range of 1900 to 24001. When breath and blood tests are performed simultaneously and the results compared, even under ideal laboratory conditions with highly trained personnel, significant troubling differences in results are consistently recorded. Breath testing is, in any event, particularly vulnerable to contamination because of the low levels involved. The traditional Breathalyzer sample, 52 mL. contains onlv 25 fie of ethanol when the BAC is O.iO%. A>y traces of alcohol trapped by dentures, any burp bringing alcohol vapors from the stomach, can have catastrophic effects. An individual whose BAC is zero, merely by taking a few appreciative sniffs over an open bottle of 50% alcohol, can send a breath tester off scale for several minutes afterward (7). Failure to save the breath sample for later independent testing effectively eliminates any hope of detecting operator error or mechanical malfunction, hut very few states require that such samples he saved, although the technology is now availahle at minimal cost.
Blood testing: Postaccident and postmoltem samples The measurement of alrohol in a given blond sample is relatively straightforward, hut methods of collection and preservation ran present problems, and correctly interpreting test results can be very difficult. Blood samples are commonly obtained in cases of serious injury or death. Samples obtained and tested by hospital
8 8 4 A * ANALYTICAL CHEMISTRY, VOL. 57, NO. 8. JULY 1985
personnel are not necessarily adequate for forensic purposes. The emergency room physician, observing an accident victim with an odor of alcoholic beverage on his breath, wants to determine 2s quickly as possible whether the ymptoms he sees are the result of a Nigh BAC or of injuries. For his purposes, a result with an uncertainty of even 50.04% may be more than adequate. To offer that same result in evidence as “the” BAC, however, may he entirely inappropriate. For forensic purposes, more careful procedures ought to he required for BAC measurements than might usually be used in routine clinical practice. Special attention must be given to documenting the chain of custody of the sample, to alcohol-free sample collection, to the use of proper anticoagulants and preservatives, and to adoption of testing procedures that ensure a high degree of precision and reliability (such as testing “knowns” before and after and running more than one test per sample). Protocols should be adopted for sample handling and test. ing and for equipment calibrations, standardizations, and maintenance, and permanent records should be kept that document all phases of sample measurement and equipment performance. Medical records must be carefully reviewed in accident and death cases. The actual injuries, and all medical treatment afforded before sample collection, or before death, must be carefully reviewed before opinions are formed about the significance of a later-test BAC. Did anything disruptive occur to raise questions ahout the true relationship of the test BAC to the actual, circulating BAC of that individual before the accident when all his normal processes and functions were intact? It has been common practice in death cases in many jurisdictions for coroners, hospital technicians, and some medical examiners to collect purported heart blood for BAC testing without an autopsy. This is done hy needle ouncture aimed throueh the chest wall at the heart. The sample collected may be “heart blood,” or only a “bloody fluid” resulting from the iniuries that caused death. When postmortem samples are submitted for BAC determinations, separate tests are not done to show the complete composition of the samde, nor are proredures followed thatwould confirm that a normal. whole-blood snmple is being tested. The results can he totally misleading. Obviously, the more extensive the trauma that has occurred. including rupture of organs and blood vessels, the more subject to gross error such “blood” sampling is. Contamination of the sample hy al-
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coho1 from the stomach, due to rupture or postmortem diffusion, is another major concern after injuries. A 10-mL sample of blood taken from an individual with a true BAC of only 0.02%(a forensically insignificant value), if it were contaminated with 1mL of stomach fluid (alcohol concentration 2%), would give an apparent BAC of 0.22%! Even when autopsies are performed, the common practice has been to collect only one blood sample for BAC purposes, which, even when collected from the intact heart can be inadequate in terms of a “reliable” BAC determination. Heart blood should be collected from the left side of the intact heart, because a substantial elevation of blood sugars frequently occurs in cases of severe trauma, shock, and sudden death, with elevations higher in the right heart than in the left. This sugar can be converted to ethanol by bacteria. This process can begin in the body before sample collection and can continue in the sample after collection and before testing. The better practice, followed by the leading forensic pathologists, is to collect a number of samples. Blood from the intact left heart, if possible, and from the femoral (leg) and cubital (arm) veins when available, should he taken so that the distribution of blood alcohol throughout the body before the accident can be confirmed. Urine, spinal fluid, vitreous humor (from the eye), and stomach contents should also be collected and tested. Even though precise relationships (i.e., between percent alcohol vitreous to percent alcohol blood) are not well defined at present, multiple sample collection and testing are important. This can effectively eliminate much later speculation as to whether a significant preaccident BAC existed or whether contamination due to injuries or other causes created false values ( 4 9 ) .In view of the importance given such evidence and the enormous legal and economic consequences, multiple samples should be required a t autopsy whenever postmortem alcohol determinations are a t issue. Reliable alcohol education, beginning a t least a t the high school level, is an essential part of any real solution to our drinking-driver problems. Anyone involved in alcohol education programs, however, should he aware of the wide range of individual responses to alcohol consumption and the deceptive nature of alcohol calculation charts and tables, which can he dangerous when relied upon by low-r men and by women generally.
Reterences (1) Fitzgerald, E. F.; Hume, D. N.Mass. Law Reu. 1981,66(1) 23. CIRCLE 50 ON READER SERVICE CAR0
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ANALYTICAL CHEMISTRY. VOL. 57, NO. 8, JULY 1985
(2) Fitzgerald, E.F.; Hume, D. N. The Champion 1983,7(10), 6. (3) Flanagan, N. G. et al. Med. Sei. Law 1979,19,180.
Widmark, E.M.P. “Die Theoretischen Grundlagen Und Die Praktische Verwendbarkeit Der Gerichtlich-Medizinischen Alkohol-Bestimmung”;Urban & Sehwarzenberg:Berlin, 1932. (5) Goldberg, L. Acta Physio. Scand. 1943, 5, Supp. 16,90. (6) Mason,,M. F.; Dubowski, K.M. J. Fo-
(4)
r e Set.~1975.20. ~ 9. (7) Spector, N. H. Science 1971,172,57. ( 8 ) Backer, R. C.; Pisano, R.V.;Sopher, I. M. J. Forensic Sei. 1980.25.327. (9) Coe, J. I. J. Forensic Sei. 1974,19,13.
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David N.Hume is emeritus professor of chemistry a t MIT. He received BA and MS degrees in chemistry a t UCLA and his PhD from the Uniuersity of Minnesota in 1943. During World War II he was section chief in analytical chemistry in a division of the Manhattan Project and afterward taught a t the University of Kansas. In 1947 he joined the faculty a t MIT, where he taught until his retirement in 1981. For the past six years his research interests have concerned the measurement and interpretation of chemical tests for intoxication and their forensic application.
1 Edward F. Fitzgerald is a trial lawyer in private practice. A member of the Massachusetts Bar, he received his J D from Boston University in 1965, and he has been admitted to practice before the Federal District Courts of Massachusetts and Rhode Island and before the US.Supreme Court. In addition to his own practice, which emphasizes civil and criminal litigation, he acts as a consultant to attorneys on serious accident and death cases inuoluing alcohol.
